Lack of genetic differentiation observed in Pacific bluefin tuna (Thunnus orientalis) from Taiwanese and New Zealand waters using mitochondrial and nuclear DNA markers

Abstract

The Pacific bluefin tuna, Thunnus orientalis, is distributed mainly in the north Pacific Ocean, but a few individuals are also found in the south Pacific Ocean. We tested the ‘one-stock’ hypothesis that genetic differentiation is absent between populations from the north and south Pacific Oceans. Three molecular markers, cytochrome (Cyt) b, control region (CR) and microsatellites, were applied to identify species, investigate the population genetic structure and infer the population demographics of T. orientalis in Taiwanese and New Zealand waters. Tissue samples of T. orientalis were collected from Taiwanese (n = 53) and New Zealand (n = 70) waters. A neighbour-joining (NJ) tree of the Cyt b gene revealed a monophyletic topology. An NJ tree of the CR showed insignificant geographical grouping. Nei’s genetic identity (0.971), FST (0.003, P = 0.243) and RST (0.019, P = 0.099) between the two sets of samples were estimated from seven microsatellite loci. A factorial correspondence analysis and assignment test showed that these two sample sets lacked genetic differentiation. All these results support the one-stock hypothesis in these two samples from Taiwanese and New Zealand waters implying that they should compose the single management unit.